FIG. 5 is a side view showing an example of a plastic plasticizing-kneading-extrusion granulator 100. The plastic plasticizing-kneading-extrusion granulator 100 shown in FIG. 5 includes a plastic plasticizing-kneading machine 101, a diverter valve 102, a gear pump 103, a molten polymer filtering device 104, a die holder 105, a die 106, and a pelletization device (UWC device) 107.
The plastic plasticizing-kneading machine 101 is a device that plasticizes and kneads solid resin. The diverter valve 102 is a device that discharges molten polymer plasticized and kneaded by the plastic plasticizing-kneading machine 101, and can switch a flow channel for molten polymer to a discharge side outside the system or the gear pump 103. The gear pump 103 is a device that transports molten polymer, and has high boosting capability with respect to large pressure loss that is generated at a device as a transport destination.
The molten polymer filtering device 104 is a device that filters out solid impurities contained in the molten polymer. The die holder 105 is a part that connects the molten polymer filtering device 104 with the die 106. A flow channel, which guides the filtered molten polymer to a plurality of holes formed at the die 106, is formed in the die holder 105. The die 106 is a part that forms the filtered molten polymer into a spaghetti shape, and a plurality of holes are circumferentially arranged on the die 106.
The UWC device 107 is connected to the die 106, and includes a circulation box to be described below. Pellet cooling/transport water (PCW) is circulated in the circulation box. The UWC device 107 forms the spaghetti-shaped molten polymer, which is continuously extruded from the holes of the die 106, into fine grains (pellets) by cutter blades that are rotated in the circulation box.
Next, the operation of the plastic plasticizing-kneading-extrusion granulator 100 will be described. In FIG. 5, solid resin is supplied to the plastic plasticizing-kneading machine 101 and is plasticized and melted by the thermal energy obtained from a barrel that can be heated and cooled and shear energy that is applied when a built-in screw 101a is rotated by a motor and a gear reducer. The plasticized and melted plastic is conveyed to the diverter valve 102, which is a downstream device, by the conveying function of the screw 101a that is built in the plastic plasticizing-kneading machine 101. The conveyed molten polymer is conveyed to the molten polymer filtering device 104 and the die holder 105 through the diverter valve 102 by the gear pump 103, and is conveyed to the UWC device 107 through die holes to be described below.
FIG. 6 is a cross-sectional view (inside view) of the UWC device 107 during the formation of pellets. The die holder 105, the die 106 including die holes 108, the UWC device 107, pellets 116, molten polymer 117, and pellet cooling/transport water (PCW) 118 are shown in FIG. 6.
The UWC device 107 includes a circulation box (water chamber) 109, a movable carriage 110, a motor (M) 111, a cutter shaft 112, a coupling 113, a cutter holder 114, cutter blades 115, a forward pressure controller 119, a backward pressure controller 120, a gap measuring unit 121, and a plate 122.
The cutter shaft 112 of the UWC device 107 is rotated by the start-up of the motor 111. At the same time, the cutter blades 115, which are fixed to the cutter shaft 112 through the cutter holder 114, start to be rotationally moved in the circumferential direction. The cutter blades 115 are moved forward or backward by a hydraulic unit or a pneumatic unit (not shown) of the forward pressure controller 119 or the backward pressure controller 120. It is possible to confirm a gap, which is formed between the die 106 and the cutter blades 115, using the plate 122 indirectly fixed to the cutter shaft 112 and the gap measuring unit 121 fixed to a housing 122a. 
The molten polymer 117, which is extruded from the die holes 108, is cut to the shape of pellets by the cutter blades 115 and is formed in the circulation box 109 in which the PCW 118 is circulated. Further, the die 106 is heated by a heating medium (steam, hot oil, an electrical heater, or the like). The UWC device 107 includes a hydraulic system (not shown), so that it is possible to fasten the circulation box 109 and the die 106.
FIG. 7 is a system diagram showing an example of a granulation apparatus 200 in the related art. The granulation apparatus 200 includes a die 106, an UWC device 107, a dehydration screen 123, a centrifugal dehydrator 124, a PCW tank 125, a PCW pump 126, a three-way valve 127, a PCW flow rate detector 128, a detector 129 for internal temperature of the PCW tank, a PCW temperature detector 130, a PCW pressure detector 131, and a manual drain valve 132.
The PCW 118 is circulated in the granulation apparatus 200 by the PCW pump 126. The pellets 116 formed by the UWC device 107 are cooled by the PCW 118 stored in the circulation box 109, are transported to the dehydration screen 123, and are separated from the PCW 118 by the dehydration screen 123 and the centrifugal dehydrator 124. As a result, pellet-like products are obtained.
The flow rate of the PCW 118 is detected by the PCW flow rate detector 128, and is adjusted by a PCW flow rate adjusting valve (not shown). Further, the temperature of the PCW 118 stored in the PCW tank 125 is detected by the detector 129 for internal temperature of the PCW tank, and is adjusted and managed so as to become a setting temperature by a PCW temperature control system (not shown). The temperature of the circulating PCW 118 is detected by the PCW temperature detector 130. The pressure of the PCW 118 during the pelletization is detected by the PCW pressure detector 131.
The following procedure is required when pelletization is started in this granulation apparatus 200.
(1) The UWC device 107 is separated from the die 106, and the die 106 is sufficiently heated by a heating medium.
(2) The plastic plasticizing-kneading machine 101 is started up, molten polymer 117 is discharged from the diverter valve 102 to the outside of the system, and cleaning (purging) is performed in the plastic plasticizing-kneading machine 101.
(3) The gear pump 103 is started up, the diverter valve 102 is switched to the gear pump 103, and it is confirmed that molten polymer 117 is uniformly extruded from die holes 108.
(4) The diverter valve 102 is switched to the discharge side outside the system, and the gear pump 103 is stopped (this state is a state where the molten polymer 117 is discharged from the diverter valve 102).
(5) The UWC device waits until a state where the molten polymer 117 is not discharged from the die holes 108, the cutting surface of the die 106 is quickly cleaned, and the UWC device 107 is connected to the die 106.
(6) The motor 107 of the UWC device 107 starts up and rotates the cutter blades 115.
(7) The rotating cutter blades 115 come into contact with the die 106.
(8) The three-way valve 127 is switched from a state where the PCW 118 is circulated on the bypass side by the PCW pump 126 so that the PCW 118 is supplied to the circulation box 109 of the UWC device 107.
(9) The gear pump 103 is started up, the diverter valve 102 is switched to the gear pump 103, and the molten polymer 117 is extruded from die holes 108 so that the pellets 116 are formed.
(10) The formed pellets 116 are transported to the dehydration screen 123 or the centrifugal dehydrator 124 by the PCW 118, and the PCW 118 attached to the pellets 116 is removed.
In the operations of (7), (8), and (9) of the above-described procedure, the PCW 118 cools and solidifies the molten polymer 117 that is present in the die 106 and the die holes 108. For this reason, there was a problem in that the molten polymer 117 is not extruded. Further, even though the molten polymer 117 is extruded from the die holes 108, there was a problem in that the molten polymer 117 is caught by the cutter blades 115. In order to avoid these problems, there is a method of making the cutter blades 115 come into contact with the die 106 before the molten polymer 117 is extruded from the die holes 108 and extruding the molten polymer 117 before the PCW 118 reaches the die holes 108 and cools the die holes 108.
However, in the above-described granulation apparatus 200, the throughput of one series of devices was about 50 t/h. For this reason, the throughput where pellets 116 having good shape can be formed without the clogging of the die holes 108 is designed to be about 25 t/h. If throughput is lower than 25 t/h, the thermal energy transmitted to the die holes 108 from the molten polymer 117 is insufficient and the temperature of the die holes 108 is lowered due to the thermal energy that is absorbed from the surface of the die 106 by the PCW 118. Accordingly, the molten polymer 117 is solidified in the die holes 108.
For this reason, it is preferable that granulation be started at 25 t/h as the throughput at the time of granulation start. However, since a large amount of molten polymer 117 is discharged from the diverter valve 102 in (4) and (5) of the granulation start procedure, many persons are required to perform the waste disposal of the molten polymer, and a large amount of plastic is scrapped. Further, many workers are concentrated in a small place, and work disorderedly. Furthermore, since feet are covered with a large amount of water and molten polymer 117, footholds are poor. This is not preferable in terms of safety.
In recent years, there has been a need for the throughput of one series of devices of 70 t/h or more. Considering the above-described contents, the throughput at the time of granulation start becomes 35 t/h or more. For this reason, waste disposal is more difficult and the amount of molten polymer 117 to be scrapped is large. Moreover, in order to pelletize a large amount of molten polymer 117, the size of the UWC device 107 is increased and the diameter of the circulation box 109 is also increased. Accordingly, a time, which is required until the circulation box 109 is filled with PCW 118 from an inlet (bottom) of the circulation box 109 to the outlet (ceiling surface) thereof, is lengthened. For this reason, since it is difficult to adjust a timing where the molten polymer 117 is extruded from the die 106 and a timing where the PCW 118 reaches the lower portion of the die 106, it is difficult to perform pelletization.
For example, in the case where pelletization is performed using the PCW 118 that is heated up to 60° C. at a bypass line, the temperature of the PCW 118 cooled by a cold pipe is lowered to a temperature lower than 60° C. when the PCW 118 reaches the lower portion of the circulation box 109. Further, if molten polymer 117 is extruded from the die 106 when the PCW 118 does not reach the vicinity of the lower end portion of the die holes 108 positioned at the lower portion of the die 106, the molten polymer 117 extruded from the upper portion of the die 106 is caught by the cutter blades 115. For this reason, a trouble where the pellets 116 cannot be formed occurs.
On the other hand, if molten polymer 117 is extruded from the die when the circulation box 109 is filled with the PCW 118, the molten polymer 117 present in the die holes 108 formed at the lower portion of the die 106 is solidified since the lower portion of the die 106 is particularly cold, so that clogging occur. If clogging occurs, the shapes of the pellets 116 become irregular and the extrusion speed of the molten polymer 117 to be extruded from the die 106 is increased. Accordingly, long pellets 116 are formed, so that yield is reduced. Further, if the incidence of clogging is increased, the pressure loss of the die 106 is increased and exceeds a design pressure. For this reason, a trouble where operation cannot be performed at a predetermined throughput also occurs.
Accordingly, in order to solve the problems at the time of the pelletization, there has been proposed a granulation apparatus including: a detection unit that detects the temperature of PCW 118 stored in a circulation box 109; and a control unit that controls the temperature of the PCW 118 stored in the circulation box 109 so that the PCW 118 stored in the circulation box 109, which is heated by the die 106, does not boil (for example, see PTL 1).
This apparatus stores the PCW 118 in the circulation box 109, controls heating so that the PCW 118 does not boil in the circulation box 109, and melts plastic present in die holes 108 by uniformly warming up the die 106. The die 106 is heated to 200 to 250° C. in order to melt plastic.